Server performace - Urgent

We have an auction site that is on a dedicated server. Currently running with php 5.6, mariadb (last version), nginx, apache. It turns out that in 10 hours we will have a big auction and the php performance is not good. At least 500 simultaneous users are expected. Server has spare capacity and we need better configuration for apache, nginx, php and mariadb in some situations. In addition we also need monitoring during the auction which will take place on July 1st from 08:00 AM to 17:00 PM